Copper wire segments as accelerator for induction furnace combustion of ferrous metal



AL 3,464,795 LERATOR FOR INDUCTION 0F FERROUS METAL arch 23. 1966 Sept 2, 1969 H. J. scHMrr ET COPPER WIRE SEGMENTS AS ACCE FUHNACE COMBUSTION Filed M Mmymfdg U.S. Cl. 23-230 5 Claims ABSTRACT F THE DISCLOSURE An accelerator for the combustion of ferrous metal samples in an induction furnace which comprises short lengths of tinned or untinned copper wire. It is preferred that the lengths be approximately equal to the diameter of said wire.

This invention relates to an accelerator for the burning of ferrous samples in an induction furnace preliminary to the analysis of various components thereof.

In the rapid analysis of iron or steel samples for certain components, a sample is withdrawn from a melt or otherwise provided, introduced into an induction furnace, exposed to a stream of oxygen, and burned. The gaseous products of combustion are thereafter carried out of the furnace by the stream of gas and analyzed in appropriate fashion. In order to speed the combustion of the sample, an accelerator has been employed which heretofore has usually been pure tin metal in small pellet form. Tin is a competent accelerator but has an unfortunate side eiect in that a copious cloud of tin oxide is evolved into the stream of transporting gas which dirties the combustion tube and clogs the dust trap.

Copper and iron chips have been used in conjunction with the tin accelerator. The iron chip additive is used to bulk up an unsuitably small iron sample, or to provide the heat source for materials, such as organic matter, which normally do not heat within an induction furnace. Copper is used to suppress to some degree the evolution of tin oxide and to reduce spitting. Apparently the copper reduces the viscosity of the melted oxides or slag, and thus permits a more ready and smoother evolution of gases. It also helps speed the combustion of such diflicultly combustible materials as stainless steel. It will be noted, however, that copper has not been used as a primary accelerator in itself.

A first object of this invention may be considered to be the provision of a copper accelerator which functions nearly as eifectively as the pure tin accelerator, or as a pure tin accelerator with known forms of copper admixed therewith, and yet which avoids the heavy oxide evolution of the tin, thereby minimizing contamination of the apparatus and the consequent need for frequent cleaning.

Another object of this invention is the provision of an accelerator of this character at exceedingly low cost.

Still another object of this invention resides in an exceedingly simple formation of this accelerator from common copper wire.

Yet another object of this invention is the provision of an accelerator of this character wherein the particle size thereof is adjusted to couple effectively to the frequency of the induction furnace so as to obtain a maximum heating eliect therefrom and proceed to combustion in minimum time.

Other objects and advantages of this invention Will be apparent from the following description and drawings, of which:

Patented Sept. 2, 1969 face FIG. 1 is a perspective view of one particle or bit of the accelerator described above;

FIG. 2 is a section taken along the line 2-2 of FIG. 1 looking in the direction of the arrows showing one form of the accelerator of this invention; and

FIG. 3 is a section through an induction furnace showing a sample contained in a crucible within the furnace, and the accelerator in association with the sample.

The accelerator of this invention is Simply described. It consists of ordinary copper wire cut into lengths 10 substantially equal to the diameter thereof. A sort of pillow-shaped structure results. The accelerator may be of tinned wire, as shown in FIG. 2, or may be uncoated wire. In FIG. 2 the numeral 12 indicates the copper core, and 14 the tin coating. The tin coating as illustrated is not to scale; the coating on ordinary clad wire is only from .00003 to .00007 of an inch.

The tin clad wire has certain advantages over uncoated wire. It is believed that even so slight a quantity of tin leads to a slightly quicker combustion of the copper. More important, it minimizes surface contamination of the accelerator on its most critical surface, i.e., the cylindrical surface. The proportion of tin, of course, is so small and so much copper is present in proportion that the evolution of tin oxide is insignificant.

FIG. 3 shows an induction furnace 16 having the exterior induction coils 18 and a liner 20. Supported therein is a crucible 22 containing a ferrous Sample 24 and a quantity of the accelerator 26. To analyze the sample, the apparatus, including the jacket 20, is purged by an oxygen stream, and the furnace is then operated to heat the sample 24 and the accelerator 26.

The sample 24 shown in FIG. 3 is a pin sample obtained by sucking a specimen of the melt into a glass tube wherein it hardens, `breaking ott the glass and cutting the pin thus obtained to a predetermined length so as to obtain a sample of known weight. An alternative practice, of course, is the use of weighed turnings or drillings for a sample. A pin sample of this character without an accelerator is considerably slower to ignite than a sample of turnings. The presence of an accelerator establishes substantially an equality of ignition time as Ibetween the two types of sample and a more rapid time than the turnings alone. Likewise, the one accelerator considered here substantially reduces the combustion time of the most ditiicultly oxidizable samples, such as stainless steel.

This sampling technique has such enormous advantages in terms of time over the use of drillings that a somewhat more difcult combustion problem is a minor consideration in comparison therewith.

A representative pin might be .56 long and .136" in diameter which would constitute a one gram sample. The accelerator used in conjunction with a sample of this character would be about 1.2 grams of the copper.

The individual metals are usually somewhat slow to heat. For reasons which follow, tin has the advantage of the lower melting point. The nature of the combustion in any case is believed to start in iron-tin or iron-copper contact areas, where, upon heating, a highly localized re active eutectic mixture is formed. With the tin, such mixture is formed at a substantially lower temperature.

It has been found, however, and this invention teaches, that the particle size of the accelerator has a major effect on its efficacy, and the selection of the proper size can bring copper to nearly the same ignition speed as tin. Assignee of this application is engaged in the development, commercial production, and sale of analytical equipment, and, in conjunction therewith, offers an induction furnace operating at about 14 megacycles. Consequently, Various sized accelerators were experimentally tested in a furnace of this frequency. The relative quantities were those described above: a one gram steel pin and 1.2

grams of copper accelerator. The described copper wire was cut into short pieces. The results were as follows:

Copper Wire .040 inch in diameter (16 mesh).

Trial No.: Seconds Copper Wire .050 inch in diameter.

Trial No.: Seconds Copper Wire (marked fine special) 0.030" dia. (2O mesh).

Trial No.: Seconds Copper powder was likewise tested and gave no combustion at all. The powder was 400 mesh.

The relative quantity of accelerator is not highly critical. With a one gram sample, from about .5 to about 1.5 grams accelerator is sufficient. Samples of one gram are usually employed for analysis. Smaller samples are bulked up with standard steels or irons. Sometimes Z-gram samples are used, in which case, the accelerator will be correspondingly increased. It is suspected that the desired ratio may be more volumetric than gravimetric in nature.

It is hypothesized that the copper particles must be greater than a certain minimum size in order to couple with the high frequency of the furnace in order to be heated thereby. On the other hand, since induction heating at eleven megacycles and upward is largely a surface effect, the greater the area-to-volume ratio, the more quickly the accelerator particles will be heated to ignition temperatures. In any case, the great advantage of the ZO-mesh accelerator will be appreciated from the table above. At 20-mesh, therefore, copper approaches very nearly the effectiveness of tin in promoting the combustion of ferrous samples, while at the same time avoiding the evolution of the tin oxide and being normally less expensive than the tin accelerator.

A further aspect of this invention resides in the use of copper wire as a source of material for the accelerator. Copper Wire is one of the least expensive forms in which copper is sold, and is commonly and cheaply available at the requisite purity. Such wire is easily sheared or clipped into short lengths by any of a variety of methods, none of which would involve invention or demand illustration. Such wire is commonly available with the above described tin coating which adds only minimally to the cost of the wire. This coating has the advantage, as stated above, of improving to a degree the performance of the accelerator, and preventing corrosion of the copper wire, which will have a deleterious elfect on the performance of the wire as an accelerator.

Another particular advantage of the wire as a source material for the accelerator lies in the fact that the cylindrical surface is held accurately to dimension. If, as stated above, the heating effect is largely a surface effect and the surface-to-volume ratio therefore significant, the two critical dimensions, or rather the cylindrical dimension, is obtainable with high accuracy at exceedingly low cost.

It will thus be appreciated that a novel and effective accelerator has been devised which substantially equals the performance of the previously known tin accelerator for aiding in the combustion of steel or ferrous samples for analytical purposes, which avoids the serious defects of the tin accelerator, and which is generally less expensive than the tin.

lt will be appreciated that this invention has two aspects: the use of copper particles of particular size as an accelerator, and copper wire as their source. As to the rst aspect, particles from any source should serve, and copper shot of the requisite size has been successfully used.

Since copper wire in whatever length or shot of whatever size can hardly be regarded as a novel product, this invention is believed best defined in the form of a method involving the new use of a known material.

Accordingly, what is claimed as new and desired to be secured by United States Letters Patent is:

1. In the method for analyzing a ferrous sample which includes introducing the sample in a crucible into an induction furnace, passing a stream of oxygen over said sample and into analytical apparatus, and operating said furnacev to neat said sample to ignition temperature, the improvement which comprises adding to said sample in said crucible as a combustion accelerator, essentially only copper in the form of short lengths of copper wire, the length resulting in a particle size of copper which couples effectively to the frequency of the induction furnace so as to obtain a maximum heating effect therefrom.

2. The method as set forth in claim 1 wherein said wire has a diameter of about .03.

3. The combination set forth in claim 1 wherein the length of said lengths of wire is substantially equal to the diameter thereof.

4. In the method for analyzing a ferrous metal sample which includes introducing the sample in a crucible into an induction furnace, passing a stream of oxygen over said sample and into analytical apparatus, and operating said furnace to heat said sample to ignition temperature, the improvement which comprises adding to said sample in said crucible as a combustion accelerator, essentially only short lengths of tinned copper wire, the length resulting in a particle size of copper wire which couples effectively to the frequency of the induction furnace so as to obtain a maximum heating effect therefrom.

S. In a method for analyzing a ferrous metal sample which includes introducing the sample in a crucible into an induction furnace, passing a stream of oxygen over said sample and into analytical apparatus, and operating said furnace to heat said sample to ignition temperature, the improvement which comprises adding to said sample in said crucible as an ignition accelerator essentially only copper particles at least partially coated with a thin coating of tin, the particles being of such a size as to couple effectively to the frequency of the induction furnace so as to obtain a maximum heating effect therefrom.

References Cited UNITED STATES PATENTS 5/1958 Dreher.

OTHER REFERENCES MORRIS O. WOLK, Primary Examiner E. A. KATZ, Assistant Examiner U.S. Cl. X.R. 23-253 

